This project continues to investigate the immune response, particularly the kinds of lymphocytes involved. We are investigating the mechanisms of activation of thymus-derived cells (T cells) in contact hypersensitivity and the mechanisms of producing immunologic unresponsiveness (tolerance) in vivo and in vitro. We are exploring T cell subpopulations and the rates of cell cycling and involvement in various aspects of cell-mediated immunity as measured by such variables as mixed leukocyte reaction, graft-versus-host reactions and response to mitogens. BIBLIOGRAPHIC REFERENCES: Claman, H. N.: Tolerance and contact sensitivity to DNFB in mice. V. Induction of tolerance with DNP compounds and with free and membrane-associated DNFB. J. Immunol. 116:704, 1976. Claman, H. N., Miller, S. D., and Moorhead, J. W.: Tolerance--two pathways of negative immunoregulation in contact sensitivity to DNFB. In Cold Spring Harbor Symp. on Quantitative Biology, XLI. In press, 1977.